Adhesion and Friction - a Study on Tactility K

Adhesion and Friction - a Study on Tactility

K ^ENNETH D ^UVEFELT

KTH Royal Institute of Technology Department of Machine Design SE-100 44 Stockholm, Sweden

Academic thesis, which with the approval of KTH Royal Institute of Technology, will be presented for public review in fulfilment of the requirements for a Doctorate of Engineering in Machine Design. Public review: KTH Royal Institute of Technology, Lindstedtsvägen 26, lecture hall F3, at 14:00 on May 27, 2016.

ISBN 978-91-7595-955-9 TRITA – MMK 2016:03 ISSN 1400-1179

ISRN/KTH/MMK/R-16/03-SE

Abstract

Although we are surrounded by hundreds of surfaces we can still distinguish them from each other simply by touch. The tactile information, interpreted by our brain and given by our fingers, is precise, but to put words to the sensation is very difficult — is it smooth, sticky or harsh? We do not only perceive surfaces differently, we also describe them differently. Luckily the forces and deformations that the skin are exposed to when sliding over a surface is ruled by laws of nature.

This thesis investigates the contact between finger and surface and how it is affected by, for example, material properties, surface texturing or changes in climate. By measuring contact area, friction coefficient, and adhesion, using different materials and under different conditions, conclusions could be drawn. Also was a model for the contact between a finger and a sinusoidal surface written, which could be used to estimate contact area, deformation and resulting friction coefficient.

Results showed how differences in for example material, surface topography and environment affect the interaction between finger and surface, and what consequences it has. If the objective is to change the feel of a surface or to alter the grip, this thesis could work as a support.

Paper A investigates the area and friction between finger and glass surface under different conditions.

Paper B presents a model for the contact area and deformation for a finger in contact with a sinusoidal surface.

Paper C is a validation of the contact area model. Here it was used on new surfaces and compared with new finger friction measurements.

Paper D mainly examines whether the adhesion or stickiness of different surfaces are distinguishable by a test panel and further how this affect the perceived pleasantness of the surface.

Paper E relates the adhesion and friction for a bioskin probe and skin.

Tests were made to evaluate how an artificial probe can be used to evaluate the tactile properties of a surface.

Keywords: Adhesion, finger, friction, humidity, material, model,

tactile friction, tactility